2011/6/19 David Bruant <[email protected]> > ** > With the current fixed properties proposal, here is what happens in the > engine at an Object.defineProperty(o, name, pd) call: > ---- > if("name" has already been observed as non-configurable){ > [[DefineOwnProperty]] (name, pd) on the fixed properties record // ES5.1 > - 8.12.9 > // This call includes invariant checking code > } > else{ > resPd = ToPropertydescriptor(call o's defineProperty trap with [o, name, > pd]); > if(!resPd.configurable){ > add "name" to fixed properties record with resPd as property descriptor > } > } > ---- > > What about doing the following: > ---- > // (Calling the trap in all cases) > resPd = ToPropertyDescriptor(call o's defineProperty trap with [o, name, > pd]); > > if("name" has already been observed as non-configurable){ > [[DefineOwnProperty]] (name, resPd) on the non-configurable properties > record // ES5.1 - 8.12.9 > // This call includes the exact same invariant checking code > > } > else{ > if(!resPd.configurable){ > add "name" to non-configurable properties record with resPd as property > descriptor > } > } > ---- > > The same amount of engine code is called and we have the genericity of > calling the defineProperty trap every single time. >
The updated strawman is already more akin to your proposed second implementation. The way I currently think about a Proxy's [[DefineOwnProperty]] method with support for fixed properties is as follows: [[DefineOwnProperty]] (P, Desc, Throw) 1. Let handler be the value of the [[Handler]] internal property of O. 2. Let defineProperty be the result of calling the [[Get]] internal method of handler with argument “defineProperty”. 3. If defineProperty is undefined, throw a TypeError exception. 4. If IsCallable(defineProperty) is false, throw a TypeError exception. 5. Let trapResult be the result of calling the [[Call]] internal method of defineProperty providing handler as the this value, P as the first argument and Desc as the second argument. 6. If ToBoolean(trapResult) is false, reject. 7. Let desc be ToPropertyDescriptor(trapResult) 8. If [[GetOwnProperty]](P) is not undefined, or desc.[[Configurable]] is false a. return [[DefineOwnProperty]](P, desc, Throw) (as per ES5 8.12.9) 9. return true
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